1. Field of the Invention
The present invention relates to an electrostatic deflector made up of (4+8m) electrodes (m=1, 2, 3, . . . ).
2. Description of Related Art
In recent years, electron-beam lithography systems have been indispensable for manufacture of semiconductor devices.
FIG. 1 schematically shows one example of such an electron-beam lithography system.
The lithography system has an electron gun 1 emitting an electron beam, a condenser lens 2 for focusing the beam onto a material 4 to be written, a deflector 5 for directing the beam at a position on the material based on data about a pattern delineation position, and a stage-driving mechanism 6 for controlling motion of a sample stage assembly 3 on which the material 4 is placed.
A controller C sends a deflection signal matched to the data about the pattern delineation position to the deflector 5 via a D/A converter 7 and via an amplifier 8. The controller C also sends a stage-moving signal to the stage-driving mechanism 6 via a D/A converter 9.
A blanking mechanism 10 consists of blanking deflectors 11 and blanking plates 12 and blanks the electron beam according to a blanking signal based on data about the pattern delineation time, the data being sent in from the controller C. The beam is emitted from the electron gun 1.
For convenience of illustration, the shown deflector 5 is only one. In practice, the deflector is composed of a deflection element for deflection in the X-direction and a deflection element for deflection in the Y-direction. Similarly, the sample stage assembly 3 consists of a stage for X-motion and a stage for Y-motion.
In the lithography system of the structure described above, when a semiconductor pattern is delineated in practice, the electron beam from the electron gun 1 is focused onto the material 4 to be patterned by the condenser lens 2. At the same time, the deflector 5 scans the beam over a desired location on the material 4 according to the deflection signal based on the data about the pattern position derived from the controller C, thus delineating a desired pattern on the material.
In charged-particle beam equipment, such as electron microscopes and focused-ion beam systems as well as the above-described electron-beam lithography system, deflectors are mounted to deflect the beam.
Such deflectors include electromagnetic deflectors and electrostatic deflectors. The electromagnetic type deflects a charged-particle beam by a magnetic field produced by electrically energizing a coil or electromagnet. The electrostatic type deflects a charged-particle beam by an electric field that is produced by applying a voltage to plural electrodes. In many electron-beam lithography systems, the electrostatic type is used which is capable of high-speed deflection because there is no hysteresis.
FIG. 2 shows a cross section of an electrostatic quadrupole deflector that is a typical electrostatic deflector.
This electrostatic defector has four pillar-like electrodes 21, 22, 23, and 24 which are identical in shape and size. The four electrodes are arranged on the same circumference such that they together form a cylindrical form. Voltages +Vx and −Vx are applied to the electrodes 21 and 22, respectively, which are opposite to each other in the X-direction. Voltages +Vy and −Vy are applied to the electrodes 23 and 24, respectively, which are opposite to each other in the Y-direction. A charged-particle beam that passes down the center axis of the cylindrical deflector is deflected by the electric field. The electric fields produced in the X- and Y-directions are controlled by appropriately adjusting the applied voltages. Consequently, the charged-particle beam is deflected in an appropriate direction.
For convenience of illustration, only deflection in the X-direction is now considered. It is assumed that voltages +Vx and −Vx are applied to the opposite electrodes 21 and 22, respectively, and that the other electrodes are grounded. The deflector itself is assumed to be symmetrical with respect to a vertical plane including the X-axis and a vertical plane including the Y-axis. The potential distribution within the deflector is given by
                              V          ⁡                      (                          r              ,              θ                        )                          =                  Vx          ⁢                                    ∑                              n                =                1                            ∞                        ⁢                                          A                n                            ⁢                              r                                                      2                    ⁢                    n                                    -                  1                                            ⁢                              cos                ⁡                                  (                                                            2                      ⁢                      n                                        -                    1                                    )                                            ⁢              θ                                                          (        1        )            where r is the distance from the center O of the deflector and θ is the angle measured from the X-axis.
In this equation, An is a constant. It is assumed that each electrode is sufficiently long in the Z-direction (in the direction perpendicular to the plane of paper) and that the potential distribution in the Z-direction is uniform.
The description provided so far applies to the potential distribution within the deflector when only deflection in the X-direction is considered. The potential distribution within the deflector when only deflection in the Y-direction is considered can be considered exactly the same.
It can be seen from this equation that the potential distribution within the electrostatic deflector contains higher-order components which cause deflection aberrations. However, it is impossible to cancel out the higher-order components in the electrostatic quadrupole deflector shown in FIG. 2.
FIG. 3 shows a cross section of an electrostatic octopole deflector. This deflector is made up of eight pillar-like electrodes 25, 26, 27, 28, 29, 30, 31, and 32 which are identical in shape and size. The electrodes are arranged on the same circumference such that the electrodes together constitute a cylindrical form. Voltages +Vx and −Vy are applied to the electrodes 25 and 26, respectively, which are opposite to each other in the X-direction. Voltages +Vy and −Vy are applied to the electrodes 27 and 28, respectively, which are opposite to each other in the Y-direction. Voltages (+Vx−Vy)/√{square root over (2)} and (−Vx+Vy)/√{square root over (2)} are applied to the electrodes 29 and 30, respectively, which are opposite to each other in a direction midway between the X- and Y-directions. Similarly, voltages (+Vx+Vy)/√{square root over (2)} and (−Vx−Vy)/√{square root over (2)} are applied to the electrodes 31 and 32, respectively, which are opposite to each other in a direction midway between the X- and Y-directions. Thus, a charged-particle beam passing down the center axis of the cylindrical deflector is deflected by the electric field.
In the electrostatic octopole deflector of this configuration, the term of n=2 of Eq. (1), i.e., r3 cos 3θ, can be canceled out. Although components of orders higher than the r3 cos 3θ are not canceled out, such higher-order components can be neglected within a range where the range of deflection is small.
FIG. 4 shows a cross section of an electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ) (e.g., m=1), i.e., 12 poles.
In this electrostatic deflector, four pillar-like electrodes 33, 34, 35, and 36 which are identical in shape and size and eight pillar-like electrodes 37, 38, 39, 40, 41, 42, 43, and 44 which are identical in shape and size are arranged on the same circumference such that all the electrodes together form a cylindrical form. Alternate electrodes 33, 37, 39, 34, 38, and 40 are X-direction deflection electrodes. A voltage +Vx is applied to the electrodes 33, 37, and 40. A voltage −Vx is applied to the electrodes 34, 38, and 39. The other alternate electrodes 35, 43, 42, 36, 44, and 41 are Y-direction deflection electrodes. A voltage +Vy is applied to the electrodes 35, 43, and 41. A voltage −Vy is applied to the electrodes 36, 44, and 42. The deflector itself is symmetrical with respect to (i) a first vertical plane including the X-axis, (ii) a second vertical plane including the Y-axis, (iii) a third vertical plane including an axis located in an angular position spaced from the X-axis in the positive (+) direction by 45°, and (iv) a fourth vertical plane including an axis located in an angular position spaced from the X-axis in the negative (−) direction by 45°.
In the electrostatic deflector of this construction, the component r3 cos 3θ can be canceled out. Furthermore, the potential components of the orders higher than r3 cos 3θ can be canceled out by increasing the number of electrodes (i.e., by increasing the number m) arranged between the electrodes 33, 34, 35, and 36 (Japanese Patent Publication No. H03-053736). The electrodes 33 and 34 are disposed about the vertical plane including the X-axis. The electrodes 35 and 36 are disposed about the vertical plane including the Y-axis. In this way, it can be said that the electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ) capable of canceling out higher-order components causing deflection aberrations is a quite advantageous deflector.
In the electrostatic deflector, a gap is formed between every two adjacent ones of the electrodes constituting the deflector, and each electrode is held to a support body made of an insulating material. In this way, the electrodes are supported and insulated from each other. However, where a beam of charged particles leaks to the side of the support body of the insulating material through the gaps between the electrodes and the support body becomes electrically charged, an electric field is produced by charging. This field leaks toward the center of the deflector through the gaps between the electrodes, exerting unwanted deflecting force on the beam of charged particles. As a result, desired deflection is done inaccurately. Accordingly, the following countermeasures have been taken.
In the deflector shown in FIG. 5, the side surfaces of the electrodes are formed in such a way that the gaps 53a, 53b, 53c, and 53d between the four electrodes 52a, 52b, 52c, and 52d are bent, the four electrodes being held to an electrode support body 51 made of an insulating material, thus preventing the beam of charged particles from leaking to the insulative electrode support body 51 through the gaps between the electrodes. In this way, the support body 51 is prevented from being electrically charged. Furthermore, if the support body 51 is electrically charged for some cause and an electric field is produced, the field is prevented from leaking toward the center of the deflector. For convenience of illustration, the electrostatic quadrupole deflector shown in FIG. 5 is equipped with antistatic means. An electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ) as shown in FIG. 4 can be similarly antistatically designed.
However, the processing providing such bent portions destroys the symmetry of the electrostatic deflector itself. Therefore, higher-order components of the potential cannot be removed in the electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ).
In the deflector shown in FIG. 6, the gaps 57a, 57b, 57c, and 57d between the four electrodes 55a, 55b, 55c, and 55d held to the electrode support body 54 made of an insulating material are partially widened. That is, holes are formed in the electrodes across the boundaries between the electrodes. Rod-like members 56a, 56b, 56c, and 56d, each made of a conductive material having a diameter greater than the width of each original gap, are inserted in the widened portions. The beam of charged particles is prevented from leaking to the insulative electrode support body 54 through the interelectrode gaps, thus preventing the support body 54 from being charged. If the support body 54 should be electrically charged for some cause, the electric field produced by the charging would be prevented from leaking toward the center of the deflector. In this way, holes are formed across the boundaries between the electrodes and extend the same distance into each of the electrodes, and the rod-like members are inserted in the holes. Because of this simple structure, the symmetry of the electrostatic deflector itself is maintained. If this antistatic measure is applied to the electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ), higher-order components are prevented from being lost.
However, where the number of poles is small as in the electrostatic quadrupole deflector shown in FIG. 6, there are no problems. If such antistatic measure is taken for the electrostatic deflector consisting of (4+8m) electrodes (m=1, 2, 3, . . . ), 12 holes each having a diameter larger than the interelectrode spacing must be formed even in the simplest case where m=1. The circumferential thickness of each electrode must be increased considerably. Therefore, the whole electrostatic deflector is increased greatly in size. If the deflector is increased in size in this way, the charged-particle beam system equipped with such a deflector is increased in size. In addition, the range of usage of the deflector is limited severely. For instance, there is a danger that the deflector cannot be used in an in-lens design having an objective lens equipped with a built-in deflector to reduce the working distance.